Register to reply

Connecting a known and unknown battery

by mike115
Tags: battery, connecting, solved, unknown
Share this thread:
mike115
#1
Mar24-08, 04:56 PM
P: 23
1. The problem statement, all variables and given/known data
An unmarked battery has an unknown internal resistance. If the battery is connected to a fresh 5.60 V battery (negligible internal resistance) positive to positive and negative to negative, the current through the circuit is 10.0 mA. If the polarity of the unknown battery is reversed, the current increases to 25.0 mA. Determine the emf and internal resistance of the unknown battery. Assume that in each case the direction of the current is negative to positive within the 5.60 V battery.


2. Relevant equations


3. The attempt at a solution
I tried making two equations using the loop rule for each setup.

5.6 - .01*r - e = 0
5.6 - .025*r + e = 0

e = 2.4 V
r = 320 ohms

Would that be right? The resistance looks a little too high to me.

When it says the batteries are connected positive to positive, does that mean the batteries are connected in series in the circuit?
Phys.Org News Partner Science news on Phys.org
Bees able to spot which flowers offer best rewards before landing
Classic Lewis Carroll character inspires new ecological model
When cooperation counts: Researchers find sperm benefit from grouping together in mice
kamerling
#2
Mar24-08, 06:22 PM
P: 456
Quote Quote by mike115 View Post

e = 2.4 V
r = 320 ohms

Would that be right? The resistance looks a little too high to me.

When it says the batteries are connected positive to positive, does that mean the batteries are connected in series in the circuit?
The answer is right. Positive to positive just means that the positive sides are connected to each other.

This has nothing to do with being in series, because the batteries will be in series no matter how you connect them.
mike115
#3
Mar24-08, 07:14 PM
P: 23
All right, thanks kamerling!


Register to reply

Related Discussions
Finding the unknown resistor using only an ohmmeter Introductory Physics Homework 5
Finding unknown matrix a, when aB=C Precalculus Mathematics Homework 4
Average speed with an unknown distance Introductory Physics Homework 2
Terminal Voltage of unknown battery Introductory Physics Homework 9